Spain's D-Day is here: the country's biggest political crisis since an attempted military coup in 1981 is about to get a resolution - one way or another - and as Bloomberg reports, Spanish police are ready to arrest Catalan President Carles Puigdemont "immediately" if he declares independence in the regional parliament, according to two people familiar with the government’s plans.

In what may be a preview of a possible upcoming civil war should today's event be handled incorrectly, Bloomberg writes that while a final decision on whether to act has not yet been taken, Spain’s National Police force has elite officers deployed in Catalonia who are prepared to join a raid if Catalan police try to shield Puigdemont. If Puigdemont makes a statement that falls short of immediate independence, the government in Madrid may stay its hand. Puigdemont has called a press conference for 1 p.m. in Barcelona.

The National Police and the Civil Guard "have sufficient officers in place to overcome any resistance they might meet" Bloomberg's sources note. A government press officer declined to comment other than to say that any such decision would have to be ordered by a judge.

Also today, Puigdemont is due to address the regional legislature at 6 p.m on Tuesday with many of his supporters looking for him to announce a new republic to follow through on the makeshift referendum held on Oct. 1. With his core supporters demanding he make good on the illegal vote for independence and officials in Madrid urging Rajoy to finally crack down on the separatist campaign, Puigdemont’s rebellion may be running out of road.

Already armed police have cordoned off the Catalan parliament, hours before the much anticipated independence speech:

Meanwhile, Spain's Prime Minister Mariano Rajoy has held a firm line, refusing to negotiate with the Catalan separatists and insisting all along that he’ll use only proportionate force in relation to the separatist government in Barcelona. Even so, prosecutors have been exploring charges of sedition against other separatist leaders including Jordi Sanchez, head of the biggest pro-independence campaign group. Sedition carries a jail term of up to 15 years.

Rajoy has vowed to use all the legal means at his disposal to prevent Catalonia seceding after Puigdemont’s government defied a series of Constitutional Court rulings to go ahead with the referendum. Catalan police ignored orders to seize ballot boxes ahead of the vote. The Spanish government has stationed thousands of National Police in cruise ships in the Port of Barcelona.

So far local asset markets are taking today's events in stride, with Spain’s IBEX stock index down just 1% as of noon in Madrid, while 10-year bond yields rose 2 bps.

Courtesy of Bloomberg, here is a flowchart laying out the various possible events in Spain over the next 24 hours.

Finally, from The Spain Report, some more details ahead of Puigdemont's much anticipated 6pm speech:

This evening at 6 p.m., Carles Puigdemont will appear before the regional parliament to discuss "the general political situation" in Catalonia. Most of the country expects that to translate as some kind of declaration of independence from Spain.

The precise wording of that statement, and to what extent it will be interpreted as a genuine declaration of independence by courts, prosecutors, the central government and Catalan separatists themselves, is unknown this Tuesday morning.

The size and reach of the Spanish state's response to any declaration of independence is also unknown: the options range from criminal charges of sedition or rebellion, through the suspension of home rule in Catalonia for an unspecified period of time and even to articles of the Spanish Constitution that allow for the declaration of a state of alarm or exception.

Given the policing shortcomings of the past 10 days, any move to arrest Mr. Puigdemont and members of his regional government would be fraught with potential difficulties.

The Catalan Police, the Mossos, have closed parliament park, the Parc de la Ciutadella, in central Barcelona, erected metal barriers around the parliament building and parked several dozen police vans outside.

The Catalan National Assembly (ANC), Omnium Cultural and local separatist groups are busy organising untold thousands of supporters to travel to the park and the area outside the High Court, in the adjacent road.

With a proven ability to mobilise several hundred thousand people, Spaniards will find out this evening if those policing efforts are enough hold back the protestors or if, in the end, they overflow into the park and surround parliament. Messaging shifted slightly overnight from "defend parliament" to "peacefully support" Catalan institutions.

Police—regional or national—were unable (national) or unwilling (regional) to stop most people who wanted to from voting on October 1, and did not stop separatist protestors from shutting down Catalan roads during a day of "total stoppage" last Tuesday.

On September 20, snap protests called by the ANC and Omnium led to the investigation of sedition because court officials and judicial police were blocked inside a building for several hours and Civil Guard SUVs vandalised.

The Spanish Home Office refused to comment on any National Police and Civil Guard provisions for the day, citing operational security requirements.